Pacific 2004 Paper

A Family of Fast Naval Ships

David J Bricknell – Vice President Systems, Rolls-Royce Marine, United Kingdom Per-Egil Vedlog – Design Manager, Rolls-Royce AS, Ship Technology, Norway

SYNOPSIS This paper describes the development of a fast monohull hull form for commercial applications and its adaptation to a class of fast naval logistics ships and fast combatants. For commercial applications the paper includes two fast Ro-Pax ships, a fast cargo ship and a fast crew boat. For naval a large fast naval sea-lift ship and a smaller inter-theatre logistics vessel are described as well as two combatant variants, a small fast attack craft and a larger fast surface combat ship. INTRODUCTION Whilst Naval ships generally became faster in the early part of the 20th century, during the latter part of the century Naval Combatants almost all delivered speeds of 25 to 32 knots and Naval auxiliary and logistics vessels speeds of around 20 knots. There were some exceptions notably a small but significant class of Fast Attack Craft at around 37 knots and some examples of hovercraft and hydrofoils at higher speeds. At the turn of the century, the Australian Navy ‘took up from trade’ a commercial fast catamaran for transport of logistics to East Timor and since then the US Army has acquired three fast catamarans and the US Marine’s one. In parallel the Scandinavian Navies of Norway and Sweden have both acquired small fast combatant craft - Skjold and Visby, and both the US Navy, with the Littoral Combat Ship, and the UK Royal Navy, with the Future Surface Combatant, are investigating faster fighting ships. Common to all these craft are high power-density mechanical propulsion systems and high-power waterjets. Less common though is the actual hull form and the construction material. Ships hull types being considered for these new fast naval ships are Surface Effect Ships, Catamarans, Stabilised Monohulls (trimarans and pentamarans), and semi-displacement Monohulls. Hull materials include composites, aluminium and high-tensile steels. This paper describes the development of a semi-displacement fast monohull that can be constructed of high-tensile steel to provide a solution to the new class of fast naval ships.

<<Figure 1 - Fast Catamaran “taken up from trade”>>

DEVELOPMENT OF THE P2500 HULL FORM During the 1990s, Rolls-Royce AS (NVC-Design) was contracted to design a Fast Ro-Pax by a commercial customer. The hull form was developed to carry a very high deadweight whilst being economically constructed largely of steel. To deliver good transport economics a very low resistance hull-form was developed incorporating a number of innovative design features; the use of waterjets and the adoption of the Rolls-Royce MT30 gas turbine propulsion system was integral to that capability. The first P2500 was a Ro-Pax of 151m, 22.4m beam and delivered 42 knots with an installed power of 64MW. The ship carried 1500 passengers, 38 trucks and 245 cars.

<<Figure 2 - Original P-2500 Ro-Pax design>> Hull lines were optimised in a systematic CFD study carried out by MARINTEK. The resulting vessel has a very slender bow shape with an extended wave-piercing type bow and a special stern shape that is designed to minimize the transom stern resistance characteristics. This is particularly important on water-jet-propelled vessels of this size and speed. The hull design has been extensively model tested thus generating very reliable resistance curves. By combining a wave-piercing bulbous bow with a mono-hull form, a longer waterline has been achieved with a very low angle of water-entrance at the bow. This has reduced resistance and minimizes slamming, while producing better motions in waves.

<<Figure 3 - tank testing at scale speed of 45 knots>>

The stern has been developed with a demi-hull shape, giving a lower base drag and reducing the effect of stern waves. This also serves to reduce wake wash problems. A stern wedge produces lift at the stern at full speed, producing a slight trim to the bow. This is favourable for reducing resistance and so increasing speed for a given power. The hull-form has a relatively low KMt, which gives a lower GM. This provides improved motions and reduced accelerations when compared to catamarans, removing the necessity for a sophisticated ride control system. The evaluation of the sea-keeping characteristics was conducted as an integrated part of the design process, and was achieved using the VERES software package developed by MARINTEK. As the vessel is very slender in design, control of the roll motions is essential; both to ensure passenger comfort and to reduce the risk of air ingestion into the outer waterjet inlets. Four roll-stabilizing fins ensure a high level of roll damping under all circumstances. The roll damping fins are also used to control the pitch motion and to reduce the speed loss in waves. Its control system includes the capability to operate the fins in such a way as to avoid excessive loads on the hull girder structure. During the design process, high focus was placed on producing a lightweight structure and extensive global longitudinal strength and fatigue studies were conducted.

<<Figure 4 - Structural model of P2500>>

Extensive dimensioning work was carried out and a detailed 3-D NAPA STEEL model was developed to verify the structural weight. This work was completed ahead of the model testing to ensure that the displacement used was accurate. On the completion of the dimensioning process, a design review was carried together with Bureau Veritas. This review was to the High Speed Code 2000, evaluating the P2500 as a passenger vessel Category B classification. Overall comparisons with ship designs in this class show that the Rolls-Royce P2500 design offers favourable powering characteristics, whilst achieving high levels of passenger comfort through improved sea keeping.

P2500 FAST CARGO VERSION This basic P2500 Ro-Pax hull form was then developed into a high-speed cargo ship of 177m and deadweight of 2500t. Twin MT30 propulsion systems gave a speed of 39 knots whilst allowing excellent range and payload options. For this size of ship, the monohull delivered lower required propulsion power than either a catamaran or an SES for equivalent payload.

<<Figure 5 - Fast Cargo Variant>> SMALL FAST RO-PAX Next in the range to be developed was the smaller Fast Ro-Pax at 133m carrying 1500 passengers. This ship achieves 38 knots with an installed power of 40 MW.

<<Figure 6 - Small Fast Ro-Pax>>

P2500 CREW BOAT The smallest of the P2500 commercial ship family is the fast crew boat. Rolls-Royce has extensive experience of providing service and supply craft to the offshore industry and it was therefore a natural progression to develop such a craft. The illustration below shows a 67m version with operating speeds of 30 knots up to 60 knots depending on the selected propulsion system.

<<Figure 7 – Fast Crew Boat>> NAVAL FAST SHIPS Rolls-Royce Marine is an organisation with a balanced portfolio of Naval and Commercial business it was therefore inevitable that consideration would be given to Naval variants of this mono-hull particularly as the ship was a sea-kindly, mono-hull and of steel construction within the capability of any Naval yard worldwide. Damage tolerance in terms of flooding or fire was therefore an inherent feature and did not compromise either payload or speed. THE FAST NAVAL SEA-LIFT VESSEL FNSLV

<<Figure 8 - The Fast Naval Sea-Lift Vessel FNSLV>>

The first Naval variant was a large Fast Naval Sea-Lift Vessel FNSLV. This ship adopted the Fast Cargo variant of the P2500 hull form at 177m delivering 4000t deadweight and lane metres of 1,800m. Naval features include a large amidships flight deck for helo operations (EH101, Chinook or Sea King), whilst leaving an open area at the stern for airlift of equipment if required without the need to drive vehicles to the flight deck. An Electronic Warfare system, Close-In weapon systems and Naval Communications provides an element of self-defence. Hangars for helicopters and fuel export to accompanying fast combatants are features that could be added to the design. The design and development of this ship is extensively covered in reference 1.

<<Figure 9 - Small scale FNSLV General Arrangement>>

INTRA-THEATRE LOGISTICS VESSEL A smaller variant of the FNSLV, based on the small Ro-Pax but with a length of only 120m has also been developed as an Intra-Theatre Logistics Vessel ITLV. Shallow draft, high-speed, large payload, steel construction and a monohull hull form ensure a flexible, robust and inexpensive ship with kindly sea motions necessary to get the troops, with their equipment into theatre and ready to fight. This ship achieves 40 knots using a combined MT30 Gas Turbine and Twin Pielstick PA6B Diesels in a CODAG arrangement for long range and excellent loiter capability.

<<Figure 10 - ITLV illustration>> FAST COMBATANTS Two Fast Combatant Variants have also been developed. The larger version is for a 5000t Fast Surface Combatant. The illustration below provides an artists impression of how such a ship might look. The platform or ‘seaframe’ consisting of P2500 low resistance, high-speed steel mono-hull and power-sense MT30 waterjet propulsion system, retains the features of the commercial P2500 hull forms but would be designed to Class Naval ship rules. The propulsion system differs however from the commercial vessels. A high-power hybrid gas turbine and electric system drive through high-performance Naval waterjets to meet the requirements for the varied operating profile of naval combatants with high installed electrical loads. This is designed to exceed 40 knots sprint with a range in excess of 4000nm at transit speeds.

<<Figure 11 - ITLV General Arrangement>>

<< Figure 12 - P2500 Combatant>> The last in the family of Fast Naval ships is the Fast Attack Craft. Agility and very high-speed are characteristics of this type of craft. Many recent craft have been around 60m in length and this suits a variant of the P2500 crew boat. Again this has been designed as a platform suitable for outfitting with the Navies, or shipyards, choice of Combat System. For this craft a Gas Turbine and Diesel CODOG system has been installed to give very high speeds. The propulsion system drives through the low signature high-performance Rolls-Royce Kamewa Waterjets developed for the Visby Class Corvette. In this configuration a small high-speed diesel provides speeds of up to 16 knots with gas turbines taking over for higher speeds. Quad MT5 GTs are used to power the ship due to their very low weight and high power and the cold-end drive configuration allowing for simpler exhaust arrangements. Two or four gas turbines can be used giving the craft very economic cruising speed and very high attack speeds. SUMMARY With an apparent convergence of technologies in high-speed commercial craft and a with a new class of high-speed naval vessels, the P2500 steel monohull offers a solution to many different naval requirements from logistics support vessels to fast combatants all from a common hull form adopting today’s technology.

REFERENCES 1. Morley J, Tate A, and Vedlog P, 2003 Development of the Rolls-Royce Fast Naval Sea-Lift Vessel (FNSLV), IMDEX 2003 2. Bricknell DJ, and Tate A, Propulsion systems for a new generation of fast naval vessels, SMI Future Waships Conference, London 2003